Obtaining higher yield and quality rapeseed protein: complex enzymatic hydrolysis assisted alkaline water extraction of cold pressed-extracted rapeseed meal

Abstract

In this experiment, rapeseed meal (RSM) was subjected to different pressing temperatures (75 °C and 150 °C) and extraction method (enzymatic hydrolysis (EH), alkaline water extraction (AWE), and EH + AWE) were chosen to assess the effects of temperature on nutritional components, protein solubility (PS), secondary structure, fractions, and molecular weight (PMW), and in vitro protein digestibility (IVPD) of RSM and various methods on the extraction rate (ER), yield, and the characteristics of rapeseed protein (RP). The results indicated that high temperature caused some proteins to remain bound within the fiber, reduced PS and α-helix content, thereby complicating the extraction process. The RP extracted using EH + AWE showed higher ER, yield, PS, small PMW, and soluble sugar, lower glucosinolate content. This study established that EH + AWE of cold pressed-extracted RSM is a suitable method for RP extraction, providing a reference for the efficient development of RSM and the application of RP in the food industry.

Keywords: Alkaline water extraction; Enzymatic hydrolysis; Enzymatic hydrolysis assisted alkaline water extraction; Rapeseed meal; Rapeseed protein; Temperature.

Fig. 1

The color, morphology and microstructure (A), FT-IR analysis (B), quantitative calculation of protein secondary structural makeup (C), ASP (D), NDI (E), and PDI (F) of HP-ERSM and CP-ERSM. HP-ERSM, hot pressed-extracted rapeseed meal; CP-ERSM, cold pressed-extracted rapeseed meal; ASP, acid soluble protein; NDI, nitrogen solubility index; PDI, protein dispersibility index. Note: In the same column, values with different letter superscripts mean significant difference (P < 0.05).

Fig. 2

The content of protein fractions (A); the SDS-PAGE analysis of HP-ERSM and CP-ERSM and their protein fractions (B: 1: HP-ERSM; 2, 3, 4: albumin, globulin, glutelin obtained from HP-ERSM, respectively; 5: CP-ERSM; 6, 7, 8: albumin, globulin, glutelin obtained from CP-ERSM, respectively), the IVPD of HP-ERSM and CP-ERSM (C) and protein fractions (D). ERSM. HP-ERSM, hot pressed-extracted rapeseed meal; CP-ERSM, cold pressed-extracted rapeseed meal; IVPD, in vitro protein digestibility. Note: In the same column, values with different letter superscripts mean significant difference (P < 0.05).

Fig. 3

The schematic diagram of rapeseed protein preparation by EH (A), AWE (B), and EH + AWE (C); the extraction rate and yield of rapeseed protein prepared by EH, AWE, and EH + AWE. EH, enzymatic hydrolysis; AWE, alkaline water extraction; EH + AWE, enzymatic hydrolysis assisted alkaline water extraction; RP, rapeseed protein. Note: In the same column, values with different letter superscripts mean significant difference (P < 0.05).

Fig. 4

The CP, ASP, NSI, PDI, GLs, RS, SS, TS of RP prepared by EH, AWE, and EH + AWE. CP, crude protein; ASP, acid-soluble protein; NSI, nitrogen solubility index; PDI, protein dispersibility index; GLs, glucosinolates; RS, reducing sugar; SS, soluble sugar; TS, total sugar; EH, enzymatic hydrolysis; AWE, alkaline water extraction; EH + AWE, enzymatic hydrolysis assisted alkaline water extraction. Note: In the same column, values with different letter superscripts mean significant difference (P < 0.05).

Fig. 5

The SDS-PAGE analysis (A, 1: Cold pressed-extracted rapeseed meal; 2, 3, 4: RP extracted by EH, AWE, EH + AWE from CP-ERSM, respectively) and IVPD (B) of RP extracted by EH, AWE, and EH + AWE. IVPD, in vitro protein digestibility, EH, enzymatic hydrolysis; AWE, alkaline water extraction; EH + AWE, enzymatic hydrolysis assisted alkaline water extraction. Note: In the same column, values with different letter superscripts mean significant difference (P < 0.05).